Investigation and modeling of creep for an all-oxide CMC

All-oxide ceramic matrix composites represent strong candidates for high temperature applications in oxidizing atmosphere, e.g. as combustion liners in gas turbines. This material class has the advantage of inherent oxidation resistance and damage tolerance, but limitations in creep resistance exist and should be included in long-term simulations of components. Data for developing a creep simulation model were acquired in creep experiments on material with quasiunidirectional fiber architecture. Besides highly anisotropic creep behavior, a significant dependence of strain rate on fiber orientation was revealed under tensile and compressive loading. Additionally, a potential size effect in compression creep was investigated by regarding different specimen’s aspect ratio. All results were evaluated with respect to stress and temperature dependences for further usage in simulations. An approach according to Hill, describing anisotropic creep, was taken as basis and modified by an own subroutine to overcome drawbacks. Hill’s model - as available in common finite element software – does not distinguish tensile from compressive creep. The new subroutine allows for a compression to tension change in stress, as well as the development of creep anisotropy caused by cumulative strain. Experimental results from tension and compression as well as from four-point bending tests were used for input and validation of the simulation.